Control system



Nov. 28, 1933. H. T. SEELEY 1,937,497

CONTROL S YSTEM Filed April 25, 1932 ITIVGfitOTI Harold T See leg His Attorneg.

Patented Nov. 28, 1933 PATENT OFFICE CONTROL SYSTEM Harold T. Seeley, Yeadon, Pa.,

assignor to General Electric Company, a corporation of New York Application April 23, 1932. Serial No. 607,203

7 Claims.

My invention relates ;to control systems and particularly to automatic control systems for asynchronous machines of the type which haveua phase wound secondary winding supplied with current of slip frequency from a separate source .and its object is to provide an improved control system of the type-disclosed and claimed in the copending application of Harold T. Seeley and George SJWhitlOW, Serial No. 607,202, filed Apr. .23, 1932, and assigned to the assignee of this application. In theabove-mentioned copending application a control arrangement is disclosedfor automatically controlling the slip frequency voltage applied to the secondary winding of an asynchronous machine in such a manner that the voltage is automatically adjusted for a predetermined time during each half cycle of the. slip frequency voltage. In order toreduce the wear on the voltage regulating apparatus, I provide an improved arrangement whereby the slip frequency voltage is adjustedfor a relatively long predetermined time once duringieachcycle of the slip frequency voltage instead of :being adjusted twice during each cycle for a relatively short predetermined time as disclosed in the'abovementioned copending application.

My invention will be better understoodfrom the following description when taken in connection with the accompanying drawing which diagrammatically illustrates a frequency I converter control system embodying my invention and its scope will be pointed out in the appendedclaims. 1 In the drawing, l represents a frequency converter comprising a synchronous machine'2 and an'asynchronous machine 3 which have'their rotors mechanically connected together. .The synchronous machine 2 has a primary winding which is arranged to be connected to an electric circuit 4 by a suitable switch 5; The synchronous machine 2 also has a field windingwhich is arranged to be connected to a suitable source of excitation 6 by a suitable switch 7. In order to simplify the disclosure, these switches 5 and 7 are shown as manually operated devices. a v

The asynchronous machine 3 has a primary winding which is arranged to be connected to another electric circuit 8 by means of a suitable switch 9. The asynchronous machine 3 also has a polyphase wound secondary winding which is connected to a suitable polyphase exciter lowhich is arranged to produce a polyphase voltage of slip frequency. As shown in the drawing, the exciter l0 isa dynamo-electric machine which has its rotor mechanically connected totherrotors of the machines 2 and 3. This machine is provided with frequency to the secondary two sets of field windings 11 and 12-andis also provided with an armature winding which is connected by means of brushes 13 to the secondary winding of the asynchronous machine 3. The field windings 11 and 12 are connected in a manner ,1 well known in the art, to two three-phase sets of adjustable brushes 14 and 15 of an ohmic drop exciter 16, the slip rings 1'7 of which are arranged to be connected to the electric circuit .8 by means of a suitable switch 18. The rotor of the ohmic drop exciter 16 is mechanically connected to the rotors of the machines 2, 3 and 10.1. The brushes 14and 15 of the ohmic drop exciter 16 are adjusted in a desired manner by means of a reversible motor 19. Since'the detail constructionofthe ",7 0

brush operating means constitutes no part of my ,7 disclosed inUnited States Letters Patent 1,778,599,

I have omitted all constructionalrdetails of'the brush operating mechanism. ,As shown in the drawing, the machineslO and 16.constitute one modification of the well known. Scherbius control system for applying an adjustable voltage of slip winding of a dynamo- 1 electric machine.

By operating the brushishifting motor 19in the proper direction while the switch 9 is .open, the primary voltage of. the machine 3 may be brought into phase with the voltageofthe circuit 8. "1 As iswell known in the art, the brush operating mechanism is also constructed so that when the primary voltage of themachine 3 and .the voltage of the circuit 8 are in' phase, ttheir winding" of themachine Band to one phase of the circuit 8 so that therelay responds to a predetermined phase relation between these. voltages. Preferably,, the relay .20 is designed to operate in accordance with the sinepof the angle between the voltages of'the two corresponding phases so that when the primaryvoltage: of the machine 3 leads the voltage of circuit 8, the re lay 20 closes its contacts 21 and 22 to effect the completion of a circuit for the motor 19 so ,that the brushes 14 and 15 are shifted in a; directionto bring the voltages into phase and when the primary voltage of'the. machine 3lags the voltage of circuit 8, therelay '20 closes its contacts 21 and 23 to effect the completion of another circooperating contacts. that the rate at which the brushes ofthe ohmic ate in one direction and the contacts 21 and 23 of the relay 2-0 control the circuit of av control relay 25 which, in turn, controls the circuits of the motor 19 so as to cause it, to operate in the opposite direction.

In order to prevent overrunning of the brush operating motor, I provide in accordance with my invention an arrangement for permitting the relay 20 to effect the operation of the brush operating motor 19 only once during eachcycle of the slip frequency voltage applied to the secondary winding of the machine 3. In the particular embodiment of my invention shown in the drawing this result isaccomplished by connecting two lialfr-wave rectifiers 2'7 and 23 in series across'two of the brushes 14 of the ohmic drop exciter 16 in such a manner that current cannot flow between these brushes through this series connection and by connecting an instantaneous voltage responsive relay 29 between the other brush 14 of the ohmic drop exciter 16 and the common connection between the two rectifiers 2'7 and'28. .With the relay 29 connected in the manner shown, it will be obvious to those skilled in the art that current flows through the relay 29 during of each cycle of the slip frequency voltage applied to the secondary winding of the machine 3. By properly designing the relay 29 so that it operates only in response .to a certain impressed voltage, it"is possible to have this relay maintain its contacts 31 open and its contacts 32cl0sed'during a portion of this period during which current flows through during each cycle of the slip frequency voltage applied to ,the secondary winding of the machine 3 one ofthe control relays is energized for a predetermined time'if the contact 21 of the relay 20 is in engagement with either of its Therefore, it will be seen drop exciter 16 are shifted varies directly with the slip frequency. i In the particular arrangement shown in the drawing a starting motor 35 is provided forstarting the frequency converter l from rest and bringing speed. It is "obvious, however, that the frequency converter maybe started in any other suitable manner, examples of which are well known in theart. As shown a switch 36 is provided for connecting the primary winding of the starting motor 35 to the circuit 4 and a starting resistor 37 is'provided incthe secondary circuit of the starting motor. This starting resistor '37 is arranged to be short-circuited by a suitable switch 38.

In order to simplify the disclosure, the switches 9, 18, 36 and 38are shown as manually controlled devices but it is obvious that they may be automatically controlled in any suitable manart.

it up to substantially synchronous auxiliary contacts 40 on the switch 18.-

The operation of the arrangement shown in the drawing is as follows: When it is desired to start the frequency converter 1, the switch 36 is closed to connect the primary winding of'the starting motor 35 to the circuit 4. After the motor 35 has reached a predetermined speed, the switch 38 is closed to short-circuit the starting resistor 37 in the secondary circuit of the motor. The switch 5 is then closed to connect the primary winding of the synchronous machine '2 to the circuit 4 after which the switch 7 is closed 1 tosynchronize the machine 2 and the switches 36 and 38 are opened. The switch 18 is then closed to connect the slip rings 17 ofthe ohmic drop exoiter 16-;to the circuit 8. The exciter 16 then operates ina manner well known in the art to apply voltage of slip frequency to the windlugs 11 and 12 "of the alternating current exciter. 10 so that a voltage of slip frequency is also applied to the secondary winding of-the frequency voltage applied to the secondary winding of the machine 3 the instantaneous voltages impressedacross the winding of the relay 29 are of such values that the relay maintains its contacts 31 open and its contacts 32 closed. 'For ex- 5 ample, if the relay is designed 1 so that its pick-up value is approximately 50% of the maximum instantaneous phase'voltage of the ohmic exciter and its drop-out valuev is approximately zero volts, the relay 29 will maintain its contacts j g 31 open and its contacts 32 closed during approximately three-fourths of each cycle ofthe slip frequency voltage. The relay 29 by opening its contacts 31 interrupts the circuit of the time relay 33. This circuit of the relay 33 also in- 15 cludes auxiliary contacts 39 on the switch 9 and the auxiliary contacts 40 on the switch 18. The relay 33 is designed in any suitable manner so that when it is energized, the contacts '41 which are in series with the contacts 32 of relay 29235 are instantly closed and. when itis deenergized the contacts are opened after the relay has been "deenergized a predetermined time. The time" setting of the relay 33 is such that the time it takes the relay toopenits contacts 41 is lessthan the minimum time the contacts 32 of relay 27 are maintainedclosed during the regulating operation. Therefore, it willb'e seen that only once during each cycleof the voltage of slip frequency applied to the secondary winding of the machine 3, the contacts 32 and 41 are connected in series for a predetermined time. Each time these contacts 32 and 41 are connected in series a'circuit is completed for the brush shifting. mo-

tor 19 if the desired phase relation does not exist n between the primary voltage of the machine-3 M and the voltage of the circuit 8. If the primary voltage of the machine 3 leads the voltage :of the circuit 8, the contacts 21 and 22 of thephase responsive'relay 20 are in engagementso that eachap; time the contacts 32 and 41 are connected in series, a circuit is completed for the control relay 24. Each time the control relay 24 is energized it completes a circuit for. the brush shifting motor 19 so that the brushes. 14 and 15 are shifted in the proper direction to decrease the lead of the primary voltage of the machine 3. This circuit of the control relay 24 also includes the auxiliary contacts 39 on the switch 9 and the the voltage of the circuit 8,,the contacts 21 and V 23 of the phase responsive relay 20 are in engagement so that each time the contacts 32 and 41 are connected in series a circuit is completed for the control relay 25. Each time this control relay is energized, it completes a circuit for the brush shifting motor 19 so that the brushes 14 and 15 are shifted in the opposite direction to decrease the lag of the primary voltage of the machine 3. The energizing'circuit of the control relay also includes the auxiliary contacts 39 on the switch 9 and the auxiliary contacts 40 on the switch 18.

When the desired phase relation between the primary voltage of the machine 3 and the volt age of the circuit 8 is obtained, the switch 9 is closed in any suitable manner to connect the primary winding of the asynchronous machine 3 to the circuit 8 and thereby interconnect the frequency converter 1 between the circuits 4 and 8. By opening its auxiliary contacts 39 the switch 9 removes the brush shifting motor 19 from the control of the phase responsive relay 20. By opening its auxiliary contacts 43, the switch 9 interrupts the circuit. of the instantaneous voltage responsive relay 29. The frequency converter 1 is now in a condition to be operated to transfer energy from one of the circuits to the other. 1

While I have, in accordance with the patent statutes, shown and described my invention as applied to a particular system and as embodying various devices diagrammatically indicated, changes and modifications will be obvious to those skilled in the art and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What'I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, an alternating current circuit, an alternating current dynamo-electric machine having a primary winding, connected to said circuit and having a phase wound secondary winding, a source of slip frequency voltage, means including'said source for applying a voltage of slip frequency to said secondary winding, means .for varying the magnitude of the voltage applied to said secondary winding and means controlled by said voltage for effecting only a single operation of said voltage varying means during each cycle of said voltage.

2. In combination, an alternating current circuit an alternating current dynamo-electric machine having a primary winding connected to said circuit and having a phase wound secondary winding, a source of slip frequency voltage, means including said source for applying a voltage of slip frequency to said secondary winding, means for varying the magnitude of the voltage applied to said secondary winding, and means controlled by said voltage for effecting only a single operation of said voltage varying means for a predetermined time during each cycle of said voltage.

3. In combination, an alternating current circuit an alternating current dynamo-electric machine having a primary winding connected to said circuit and a polyphase secondary winding, means including a polyphase source of slip frequency voltage for energizing said secondary winding, means for varying the excitation of said secondary winding, and control means for said excitation varying means including two halfwave rectifiers connected in series between two phase terminals of said source in such a manner as to prevent the flow of current through said series connection; and a relay having a winding interconnected between the common connection of said rectifiers and a phase terminal of said circuit.

4. In combination, an alternating current circuit an alternating current dynamo-electric machine having a primary winding connected to said circuit and a polyphase secondary winding, means including a three-phase source of slip frequency voltage for energizing said secondary winding, means for varying the excitation of said secondary winding, and control means for said excitation varying means including two half- .wave rectifiers connected in series between two phase terminals of said source in such a manner as to prevent the flow of current through said series connection and a relay having a winding interconnected between the other phase terminal of said circuit and the common connection of said rectifiers.

5. In combination, two alternating current circuits, two dynamo-electric machines having their rotors mechanically connected together, each machine having a primary and a secondary winding, means for connecting the primary winding of one of said machines to one of said circuits, means for applying a voltage of slip frequency to the secondary winding of the other machine including an ohmic drop exciter having its rotor mechanically connected to the rotors of said machines, said exciter including a plurality of adjustable brushes, and means for controlling the adjustment of said brushes including two halfwave rectifiers connected in series between two of said brushes and a relay having a winding interconnected between one of said brushes of said exciter and the common connection of said rectifiers.

6. In combination, two alternating current circuits, two dynamo-electric machines having their rotors mechanically connected together, each brushes, and means for controlling the adjustment of said brushes including two half-wave rectifiers connected in series between two of said brushes and a single phase instantaneous voltage responsive relay having a winding interconnected between the third brush of said exciter and the common connection of said rectifiers.

'7. In combination, a three-phase circuit, two half-wave rectifiers connected in series between two phase conductors of said circuit in such a manner as to prevent the flow of current through said series connection, and a single-phase instantaneous voltage responsive relay interconnected between the common connection of said rectifiers and the other phase conductor of said circuit.

HAROLD T. SEELEY. 

